The real reason Mind Spike is kind of weak is because Lightning Rush (and to a lesser degree Forceful Reversal) exists. In most cases, the Battlemind's own 2W+Con damage from an augment-2'ed LR will equal or exceed the target's single-hit damage that Mind Spike would deal, LR can't be avoided by shifting away or even by including the Battlemind in the attack, and LR actually protects an ally instead of avenging them. Simply put, as soon as you hit level 7, a Battlemind will essentially never again use Mind Spike because they'll have Lightning Rush and it's simply a better use of their immediate actions (and their power points).